Method for the continuous transferring of liquid metals or alloys into solid state with desired cross section without using a mould



United States Patent O ABSTRACT OF THE DISCLOSURE Continuous casting technique, wherein a sheet of metal is continuously moved downwardly whilst opposite edges are welded together; the envelope is supported between opposed rollers; molten metal continuously poured into resulting descending tubular envelope; a first set of sprays of coolant is directed onto upper zone of wall of filled envelope under conditions to produce moderate cooling of contents, after which second set of sprays of coolant is directed onto lower zone of rwall of filled envelope under conditions to effect fast cooling. Filled envelope is moved downwardly and away at the rate tubular envelope is formed and filled.

This invention relates to the continuous casting of molten metals.

Hitherto metals have been continuously cast by pouring a melt into a straight or curved mold. The mold which was open both at its upper and lower ends, Iwas radially cooled. By a suitable method of cooling and design of mold a shell of solidified metal was formed around the casting before it left the mold. The shell was supported around the still liquid interior of the casting until, upon further coolin the casting became completely solid. The shell had poor physical and mechanical properties. It was short and brittle, on account of its primary structure, and of any oxidation that occurs, and of diffusion of the material of the mold into the shell. The shell also had slag and oxide inclusions. Because of these factors, there was a tendency, when ordinary bending strains occurred, for cracks to be produced in the shell followed by seepage of the still-liquid core.

The conventional mold required a complicated mechanism for oscillation to prevent adhesion of the shell; was exposed to hard wear; and required frequent replacement. The mechanism for fwithdrawing the closure mechanism from the bottom of the mold was complicated and expensive because of the need for precise coordination if a reasonable product were to be produced. Because of the use of a mold this method was not applicable where products of varying cross-section were required. Moreover, tlie metal contracted as it is cooled and the lower part of the mold was thus not necessarily in contact with the metal. This led to a reduction in the cooling efficiency of the lower part of the mold.

Rapid cooling of the strand leaving the mold is undesirable and therefore axial cooling of the strand, which provides a better product than radial cooling, could not be employed. The physical properties of the product as produced 'were not good. Radial cooling of the metal produced a transcrystalline product which was not conductive to further treatment. As the casting left the mold there was a sharp change in the cooling rate with a consequent tendency for longitudinal cracks to occur at this point.

The use of the mold also placed a limit on the minimum dimensions of the product. This means that further "ice treatment was necessary if a product below these minimum dimensions was required.

As a result of these and other factors, previous methods for the continuous casting of metals have not been entirely satisfactory.

According to the present invention there is provided a method for the continuous casting of a molten metal, comprising the continuous production of -a substantially vertical tubular envelope from sheet metal; supporting said envelope at at least two opposite portions; continuously pouring molten metal into the upper open end of the descending tubular envelope; directing a first set of fiuid coolant sprays onto an upper zone of the wall of the envelope to produce an initial moderate cooling of the metal; as soon as the envelope and` contents have descended below said support directing onto the Iwall of the envelope a second set of fluid coolant sprays under conditions to effect a vigorous cooling of the metal therein; and moving the envelope and solidifying metal therein generally downwardly and away at :a rate corresponding to the rate of pouring and to the rate of production of the envelope.

The present invention further provides apparatus for the continuous casting of a molten metal, comprising means for the continuous production of a substantially vertical tubular metallic envelope, means for supporting said envelope at at least two opposite portions, means arranged for pouring metal into the upper open end of the envelope, a closure arrangement for the lower end of the envelope, an upper first set of coolant spraying means, a lower second set of coolant spraying means, and a dra-wing mechanism adapted to move the envelope and solidifying metal therein generally downwardly and alway at a rate corresponding to the rate of pouring and to the rate of production of the envelope.

The invention is herein after more particularly described by way of example only with reference to the accompanying drawing, in which The single figure of drawing diagrammatically illustrates the process of the present invention and in the illustrated apparatus, sheet metal 2 which should be free of defects, is caused to pass over rollers 6 from drums 5. The several sheets are joined or welded by known methods as at 3 to produce an envelope. In the illustrated arrangement the envelope is made up of four sheets which are welded "together to form an envelope having a rectangular cross section. However, Iby a suitable choice and arrangement of sheets, rollers, and joining techniques, -a wide range of envelope cross sections are possible. For example, it may be preferable to use two sheets welded to form an evelope with a circular or oval cross section.

,Initially the end of the envelope is closed by a closure Amechanism or dummy bar which may be similar to that commonly used in conventional continuous casting. The closure mechanism is coupled to drawing mechanism (not shown).

The melt is poured from a tundish 1 into the envelope, and solidifies first at the closure mechanism. As the closure mechanism is drawn away by the drawing mechanism the envelope and solidifying metal is caused to pass between a series of rollers. The rollers 7 should preferably be relatively friction-free and should support the envelope on at least two sides. Rollers 7 are cooled by spray nozzles 4a and 4b. The cooling effect of spray nozzles 4a is arranged to be relatively slight to avoid an initial cooling shock, whereas the cooling effect of nozzles 4b may be somewhat greater.

The solidifying casting is withdrawn by the Idrawing mechanism on support rollers 8 at a rate corresponding to the rate of pouring and the continuous joining together of the sheets 2 to form the envelope. The support rollers 8 :may be arranged in a straight or curved line, and may be cooled by further spray nozzles 4b as shown. The casting is withdrawn for further processing, as for example rolling, winding or bending, for cutting and/ or for stocking.

The method of cooling employed ensures that the major direction of heat transfer is along the length of the casting. Initial cooling is at the closure mechanism and not as with previous continuous casting methods, using a mold, at the level of the melt. The support rollers need only be cooled to an extent sucient to guarantee the strength of the envelope but not to solidify the core 9 of the casting. The casting is thus initially solidied only slightly, as at 10a, and is increasingly solidified as at 10b as it is withdrawn.

The solidifying casting is withdrawn by the drawing mechanism at a rate corresponding to the rate of pouring and the continuous joining together of the sheets 2 to form the envelope. The support rollers may be arranged in a straight or curved line, and may be cooled by further spray nozzles 4b as shown. The casting is withdrawn for further processing, as for example rolling, winding or bending, for cutting and/or for stocking.

The method of cooling employed ensures that the major direction of heat transfer is along the length of the casting. Initial cooling is at the closure mechanism and not as with previous continuous casting methods, using a mold, at the level of the melt. The support rollers need only be cooled to an extent sufficient to guarantee the strength of the envelope but not to solidify the core of the casting. The casting is thus initially solidified only slightly, and is increasingly solidified as it is withdrawn. The only slight cooling of the support rollers may be ensured by the use of steam at the spray nozzles. Predominantly axial cooling and relatively slight radial cool- I ing avoids transcrystallization, and the tine crystalline structure produced as a result is particularly conducive to further treatment such as rolling.

The sheet envelope has a secondary structure with a high ductility and is free from defects such as oxide inclusions and cracks, and is thus in every way superior to the initial solidified shell produced in conventional continuous casting techniques. Depending on the chemical composition of the melt, the envelope may consist of the same material as the melt, or of another material. It advantageously may be of cheap and second rate quality.

With previous continuous casting techniques, timeconsuming and expensive surface treatment, such as grinding or planning, was often required. The present method practically eliminates these. The envelope is a protection against oxidation yduring further heat treat. ment. The envelope may be detached during working of the product (for example rolling), and can be collected and remelted. To avoid adhesion of the sheet to the casting, thin layers of oxides or the like may be applied to the inside of the envelope. When it is not desired to remove the sheet envelope, and when perfect adhesion is required, as for instance for plating, the melt is supplied with oxide solvents such as the halides of alkali metals or mixtures bet-Ween these and rare earth kmetals and salts thereof. The oxide solvents should be easy to melt but not easily drawn into the ymetal of the melt. This method dissolves the ordinary surface oxidation of the envelope just above the level of the melt so that good adhesion of the melt to the envelope is produced. The use of degassing techniques mainly with inert gases, for example vacuum degassing, facilitates adhesion.

I claim:

1. A method for the continuous casting of a molten Imetal, comprising continuously moving at least one sheet of metal in a downward direction while uniting adjacent edges of the sheet by welding to form a vertical tubular `metallic envelope; supporting said tubular envelope at at least two opposite portions by means of rollers to ensure an easy downward movement of said tubular envelope; continuously pouring molten metal into the upper end of the downwardly moving tubular envelope; directing a tirst set of sprays of a fluid coolant onto a first upper zone of the walls of said tubular envelope to produce a moderate cooling of the metal therein; directing a second set of sprays of a fluid coolant onto a second lower zone of the walls of said tubular envelope to produce a vigorous cooling of the metal therein; and moving the tubular envelope and the solidifying metal therein generally downwardly and away at a rate corresponding to the rate of pouring and to the rate of production of the tubular envelope.

2. A continuous casting method in accordance with claim 1, in which the cooling of the liquid metal present in the sheet ,metal envelope is made to take place mainly axially by initial moderate cooling of the envelope and the metal of the support arrangement to conserve the necessary strength of the sheet metal envelope, and in which the envelope is subjected to a vigorous cooling first when leaving the support arrangement, whereby the crystals of the resulting casting attain a generally axial orientation.

3. A method according to claim 1, wherein a layer of oxide is applied to the surface of the material of the envelope to avoid adhesion to the casting.

4. A method according to claim 1 wherein oxide solvents are added to the melt to dissolve any surface oxidation of the envelope and enable adhesion of the envelope to the casting.

References Cited UNITED STATES PATENTS 2,264,457 12/1941 Roth 164-86 X 2,310,893 2/1943 Brenner 164-86 2,692,411 10/1954 Brennan 164-86 X 2,698,467 1/1955 Tarquinee et al. 164-283 X 3,163,896 1/1965 Rochester et al. 164-73 3,349,832 10/1967 Crowdes et al. 164-86 FOREIGN PATENTS 884,516 4/ 1943 France.

740,458 10/ 1943 Germany.

744,116 l/ 1944 Germany.

509,456 7/1939 Great Britain.

495,990 11/1938 Great Britain.

I. SPENCER OVERHOLSER, Primary Examiner. R. S. ANNEAR, Assistant Examiner. 

